Anthrax is an acute disease caused by the bacterium Bacillus anthracis (B. anthracis). Most forms of the disease are lethal, and it affects both humans and animals. B. anthracis exerts its toxicity via the dissemination of a tripartite exotoxin comprised of protective antigen (PA), lethal factor (LF) and edema factor (EF). PA plays a critical role in anthrax pathogenesis, where it can associate with either LF to form lethal toxin (LeTx) or with EF to form the edema toxin (EdTx).
Antibiotic therapy is effective for the treatment of anthrax when administered soon after infection and before the onset of symptoms. Yet, due to the possible long-term survival of anthrax spores in the lungs, a prolonged antibiotic treatment period was recommended (1). However, antibiotic treatment/prophylaxis can be problematic in situations where their use is contraindicated, or in cases involving antibiotic resistant B. anthracis strains (2). Furthermore, in cases where disease has progressed and a substantial amount of anthrax toxins have been delivered to the bloodstream, antibiotic treatment is of less value, highlighting the need for additional post-exposure treatment (2).
Currently, the updated recommendations of the Centers of Disease Control and Prevention (CDC) following potential exposure to aerosolized B. anthracis spores include a prolonged antibiotic treatment period (at least 60 days) combined with active immunization against PA (3).
Several antibodies directed against PA were isolated and described to date, for example in the U.S. Pat. No. 7,456,264 (4), GB 2480298 (5) and U.S. Pat. No. 7,601,351 (6). Rosenfeld R. et al. (7), Mechaly A. et al. (8), and Mazor O. et al. (9), the content of each of which is incorporated herein by reference, describe the isolation and activity of the monoclonal antibody mAb 29 and its corresponding human IgG1-based chimeric antibody (cAb29), although the antibody reported in these publications was not made available to the public and there was no description of the sequence of any part of such antibody. The mAb 29 and cAb29 antibodies reported in these publications are the same antibodies which have been sequenced, described, and claimed herein. Only the present specification describes these specific antibodies in sufficient detail to place them into the hands of the public.